Composite panel projectile barrier

ABSTRACT

A projectile barrier comprising a plurality of spaced sheets of tough resilient plastic material, adjacent pairs of said sheets having interposed between them strips of resilient plastic material extending around the periphery thereof and sealed to said sheets to provide a hermetically sealed enclosure between the sheets, said enclosure being filled with air or other inert dry gas, said barrier functioning to resist penetration by bullets or other projectiles by virtue of the energy absorbing properties of the gas-filled chambers formed between the plastic sheets in addition to the inherent toughness of the sheets themselves. The structure also has advantages as a light-weight acoustic barrier for the attenuation of sound waves.

United States Patent 1 1 .1111 3,872,804 Yarnall 1 Mar. 25, 1975 1 1 COMPOSITE PANEL PROJECTILE 3,700,554 10/1972 Cook 161/404 x BARRIER 3,745,938 7/1973 Hathaway et a1, 109/495 [75] Inventor: Donald 1; Yarnall, Ambler, Pa. EIG ATE TS 0R APPLICATIONS 73 Assignee: Commercial Plastics & pp y Co. 759,911 12/1933 France 52/203 Inc., Cornwells Heights, Pa,

' Primary ExaminerDennis L. Taylor [22] Filedi Sept 1973 Attorney, Agent, or Firm-Allen V. l-lazeltine [21] Appl. No: 400,450

Related US. Application Data 1571 ABSTRACT [63] Continuation-in-part of Ser. No. 182,397, Sept. 21, A projectile barrier comprising a plurality of spaced 1971. sheets of tough resilient plastic material, adjacent 1 pairs of said sheets having interposed between them [52] US. Cl. 109/49.5, 109/84 strips of resilient plastic material extending around the [51] Int. Cl. F41h 5/08 periphery thereof and sealed to said sheets to provide [58] Field of Search 109/80, 78, 82, 84, 49.5, a hermetically sealed enclosure between the sheets,

109/585; 52/171, 616; 244/129 W; 161/404, said enclosure being filled with air or other inert dry 45, 183 gas, said barrier functioning to resist penetration of bullets or other projectiles by virtue of the energy ab- [56] References Cited sorbing properties of the gas-filled chambers formed UNITED STATES PATENTS between the plastic sheets in addition to the inherent 2,025,770 12/1935 Parkinson et a1. 52/398 toughness of the Sheets themselves- The Structure also 2,332,060 10/1943 Colleran 2,602,970 7/1952 Gouge.....'.... 52/203 the attenuatwn Of Sound Waves- 3,399,294 8/1968 Thieben 52/171 X 3,630,814 12/197, '1 Arnold 161/404 X 7 Claims, 5 Drawing Figures I 52/171 has advantages as a light-weight acoustic barrier for 1 COMPOSITE PANEL PROJECTILE BARRIER" This application is a continuation in part of my copending application Ser. No. 182,397, filed Sept. 21, 1971.

This invention relates to improvements in projectile barriers, and in particular to such barriers which, although light in weight, are extremely effective in resisting the passage through them of projectiles, and which if desired may be transparent so as to be usable as windows.

It is known to provide opaque projectile-resistant barriers of specially constituted alloy steel. It also is known to provide transparent projectile-resistant barriers of specially constructed laminated glass. Because of the considerable weight involved, neither of these forms of projectile barriers is well adapted for certain applications, including particularly those involving mobility.

Accordingly, it is an object of the present invention to provide a relatively light form of projectile barrier which may be either opaque or transparent, and which nevertheless is capable of providing high resistance to penetration by high velocity and relatively large projectiles.

In accordance with the invention there are provided a plurality of spaced sheets of tough resilient plastic material, adjacent pairs of such sheets having interposed between them strips of resilient plastic material extending around the entire periphery thereof and sealed to said sheets to provide a hermetically sealed enclosure between the sheets, said enclosure being filled with air or other inert dry gas. The structure thus formed is such that the resilient plastic sheets are free to flex under impact of an impinging projectile and their own inherent toughness provides a certain measure of resistance to passage of an impinging projectile through them. In addition, the air or other inert gas enclosed in the space between adjacent plastic sheets provides a compressible medium which is capable of dissipating energy in response to flexure of the plastic sheets caused by an impinging projectile. In some instances a single pair of sheets, forming a single enclosure between them, is sufficient to prevent the passage through the barrier of projectiles of moderate velocity and size. Even though the projectile may penetrate the first plastic sheet and pass into the space between it and the second sheet of the pair, sufficient of the energy thereof may be dissipated by the combined action of the first sheet itself and the compression of the air or other gas enclosed betweenthe pair of sheets to prevent passage of the projectile through the second sheet.

I am aware of prior proposals of projectile barriers (such, for example, as that contained in U.S. Pat. No. 3,630,814 granted Dec. 28, I971 to Alfred Arnold) employing spaced glass panels separated at their peripheries by rigid metal spacing strips and provided with elastic edge seals of silicone rubber. Such structures are not capable of providing the advantages in accordance with the present invention because their use of rigid metal edge spacers prevents the achievement of a freely flexible structure and because the silicone rubber seals will not withstand the impingement of high ve locity projectiles without rupturing. Hence such structures do no afford the energy absorbing advantages achievable in accordance with the present invention as referred to above.

In another form of the invention, adapted to resist penetration by projectiles of higher velocity and/or size, there may be provided a multiplicity of sheets forming a multiplicity of compression chambers between adjacent sheets so that even if the projectile penetrates both sheets of a first pair, subsequent pairs and the compression chambers formed between them will be effective to further dissipate the energy of the projectile and prevent penetration through the over-all barrier. Thus the barrier structure may be designed with a sufficient number of resilient plastic sheets and intermediate compression chambers to resist the passage of any desired velocity and size of projectile within selected limits. Y

The invention will be more fully understood from a consideration of the following detailed description with reference to the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view ofa projectile barrier in accordance with the invention;

FIG. 2 is a fragmentary sectional view taken along line 2-2 in FIG. 1;

FIG. 3 is a fragmentary sectional view of another form of the embodiment of FIG. 1;

FIG. 4 is a detailed sectional view showing the structure of the edge portion of the embodiment of FIGS. 1 and 2; and

FIG. 5 is a sectional view showing a further modification of the structure in accordance with the invention.

Referring now to FIG. 1 there is shown a pair of spaced resilient plastic sheets 1 and 2 defining a space 3 between them which may be filled with air or any desired inert gas such, for example, as nitrogen or argon. The resilient plastic sheets 1 and 2 preferably are formed of polycarbonate, but may be of any other suitable plastic material'such as polyethylene, polyvinyl chloride, a vinyl chloride-acrylic copolymer, polystyrene, styrene-butadiene copolymer, polymethyl methacrylate, hexamethylenediamine-adipic acid copolymer, phenyl-formaldehyde resin, ureaformaldehyde resin, a polyamide, polypropylene, ethylene-propylene copolymer, a vinyl chloride vinyl acetate copolymer, a phenylene oxide polymer, an ionomer (i.e. polymer in which ionized carboxyl groups create ionic crosslinks in the intermolecular structure), or polyurethane. As shown, the two plastic sheets 1 and 2 are maintained spaced from each other and hermetically sealed at their edges by a strip of resilient material, preferably polychloroprene (neoprene) or other suitable material such as polybutadiene, isobutylene-butadiene copolymer, silicone, polyurethane in either solid or foam form, or an epoxy. Resilient strip 4 is interposed between the plastic sheets 1 and 2 and hermetically and resiliently sealed to them by a compatible elastomer such as one of the so called barge or contact cements, one of the high strength cyanoacrylate adhesives or an epoxy cement. This strip preferably may be of T cross-section as shown more clearly in FIG. 2 and in the detail diagram of FIG. 4, but other forms may be used if desired. It is important to the achievement of the results in accordance with the invention that the material used for this spacing and sealing strip be resilient so as to provide for flexure of the plastic sheets I and 2 under projectile impingement, and also that it be well sealed to the plastic sheets to provide a strong and gas-tight seal.

Lower alkyl cyanoacrylate adhesives, such as ethyl and methyl cyanoacrylate, are especially suitable for use in sealing strip 4 to sheets I and 2 in accordance 3 with the present invention. Particularly suitable adhesives of this type include Permabond 101 and 102. The characteristics of these ethyl cyanoacrylates are set forth in the following table:

Another preferred cyanoacrylate is Eastman 910 which is methylalpha cyanoacrylate.

Polyepoxides which can be used as adhesives in the present invention are primarily polyfunctional glycidal ether type epoxy resins. Preferred polyepoxide compounds are glycidyl ethers of polyhydric phenols, such as diphenylol alkanes, e.g., diphenylol propane, diphenylol ethane and diphenylol methane, diphenylol sulphone, hydroxyquinone resorcinol, dihydroxydiphenyl dihydroxynaphthalenes and resins, such as novolacs and resols, which have been prepared by condensation of phenol and formaldehyde. Epoxy resins of the epichlorohydrin bisphenol A type are particularly preferred.

Glycidyl ethers of polyhydric phenols can be prepared in various ways, for example by reaction of the polyhydric phenol with epichlorohydrin in the presence of a base such as sodium hydroxide or potassium hydroxide. Important polyepoxy compounds are the glycidyl ethers of 2,2-bis (4-hydroxyphenyl)-propane. The molecular weight, as well as the softening point and viscosity of such compounds, generally depend on the ratio of epichlorohydrin to 2,2-bis(4-hydroxyphenyl) propane. If a large excess of epichlorohydrin is used, e.g., l0 molecules of epichlorohydrin per molecule of 2,2-bis(4-hyclroxyphenyl) propane, the main component in the reactionproduct is a glycidyl ether of low molecular weight. In some instances, polyethers can contain small amounts of material with a terminal glycidyl radical in hydrated form. Glycidyl polyethers of 2,2-bis (4-hydroxyphenyl) propane having a molecular Approximate Epoxide Resin Equivalent Molecular Weight Viscosity Epon 812 140-160 306 1-2 poises Epon 826 180-188 65-95 ioises Epon 828 185-192 390 100-160 poises Epon 832 230-280 470 4-9 poises Dow 33] 192 390 A particular preferred epoxy adhesive is Eccobond 45LV which has the following properties:

Uncatalyzed viscosity, cps 35,000 Hardness (Shore Durometer) 40 Bond Strength in Shear at Room Temperature. psi 3.200 Flexural Strength, psi 5,500

Anhydrides, primary amines or secondary amines can be used as accelerators for the epoxides and tertiary amines can catalyze these epoxy materials. Catalysts, such as methylphenyl diamine, diethylene triamine and triethylene tetraamine are preferred.

Contact adhesives can also be employed in the present invention. Such adhesives include polychloroprene, phenol formaldehyde resin, and vinyl acetate-phenolic copolymer. Preferably such adhesives are used in conjunction with a solvent such as methyethyl ketone, or methylhexyl ketone, plus xylol and/or toluol. A specific example of contact cement is SCOTCH-GRIP 1357 which is polychloroprene present in a ketone solvent having a viscosity of 225 cps, a flashpoint of l4F., a solids content of approximately 25% and a Brookfield viscosimeter reading of RVF lsp. at 20 rpm.

The thickness of the resilient plastic sheets 1 and 2 and their spacing is chosen to achieve the desired compressibility characteristics of the chambers formed between sheets to achieve maximum absorption of energy of impinging projectiles as will be discussed hereinafter. In general, the thickness of the sheets and their spacing will vary depending upon the over-all area of the barrier. For example, a sheet thickness of onequarter inch has proven effective for barrier areas between 1 square foot and 6 square feet and may be increased to three-eighth inch for barrier areas between 6 square feet and 32 square fee, and to one-half inch for barier areas between 32 and 64 square feet. Similarly, for barrier between 1 square foot and 4 square feet, panel spacing may be one-quarter inch, for barrier areas between 4 and 16 square feet the spacing may be increased to one-half inch, and for larger areas up to 64 square feet, the spacing may be increased to 4 inches.

In general, it will be understood that the flexing of theplastic sheets is fundamental to the projectile resistance of the barrier, and they should not be made so thick as to render them substantially unyielding under projectile impingement.

When a projectile impinges, for example, on the outer surface of the plastic sheet 1, it will cause that sheet to be deformed inwardly in the direction of the space 3 between sheets 1 and 2. Because of such deformation, the plastic sheet 1 will tend initially to resist penetration by the projectile both because of its inherent toughness and also because of dissipation of the energy of the projectile as the plastic sheet 1 deforms and compressed the gas enclosed in the space between plastic sheets 1 and 2. Nevertheless, if the energy of the projectile upon impingement is sufficiently high, it may pass through the plastic sheet 1 into the space 3 between sheets 1 and 2. However, having lost a considerable amount of its energy, it may have insufficient remaining energy to pass through the second plastic sheet 2 and therefore will not traverse the entire barrier structure and will do no harm to persons on the other side of the barrier.

The operation of the foregoing arrangement may be further described in the following manner:

1. Upon impingement of a projectile on one of the plastic panels of the structure, energy is distributed over a larger area than the point of impact or over the entire first surface which is commonly larger in the order of 35,000 to l than the area actually impacted by the projectile (i.e., 0.357 inch diameter to l 152 square inches in a 24 inch by 48 inch panel).

2. Compression of the gas enclosed between the panels occurs immediately adjacent to the first panel and the resultant pressures are distributed over the interior surfaces of the panels and their edge sealing strips.

3. In many cases this distribution of initial impact energy effectively stops such a common load/caliber as 0.38 Special commercial ammunition and often bounces it back toward the source.

4. When load/Calibers of a higher order of energy secondarily penetrate the first face, they do so only after momentarily dissipating a substantial portion of their total energy and they are stopped and trapped by the second or successive layers and compression chambers (i.e., 0.357 magnum, lead commercial loads are commonly entrapped in the first chamber and do not penetrate through the second solid member).

Referring now to FIG. 3, there is shown a modification of the structure of FIG. 1 in which four plastic sheets, 1, 2, 5 and 6 are provided, each spaced from the adjacent sheets by the spaces 3. This structure is adapted to provide even greater resistance to penetration by projectiles of higher velocity and size as will be readily apparent, the mode of operation nevertheless being essentially the same as that of the two-sheet structure of FIGS. 1 and 2. In the arrangement of FIG. 3, even though the projectile may be of such velocity and magnitude as to penetrate both plastic sheets 1 and 2, its velocity will be further reduced by the compression of the gas in the space between sheets 2 and 5 and subsequently by compression of the gas between sheets 5 and 6, as well as by the inherent resistance to penetration afforded by sheets 5 and 6. It will be noted that the four plastic sheets 1, 2, 5 and 6 in the embodiment of FIG. 3 are sealed at their edges by a strip similar in form to that used in the embodiment of FIGS. 1 and 2 but comprising multiple spacing portions extending between the adjacent plastic sheets.

While the invention has been described with particular reference to its usefulness as a projectile barrier, it also has very substantial'usefulness as an acoustic barrier for the attenuation of sound waves. This is particularly so with reference to forms of the invention in which the edge sealing and spacing strips are composed of materials of the sort hereinbefore mentioned in foam or cellular form in particular such materials as po1yurethane and the like. In such structures it appears that the principle of operation acoustically is very similar to that in the case of their projectile-resistant properties. That is, through the compression of the gas enclosed within the chamber or chambers between adjacent plastic sheets, sound energy is dissipated and is absorbed in the edge sealing and spacing strips, this action being particulary effective when the sealing and spacing strips are made of a suitable material in cellular form. It has been demonstrated by tests that the acoustic performance of such barriers is at least as good as, and in many cases superior to. the performance of conventional multi-pane glass structures. However, the structure in accordance with the present invention is much lighter and therefore much more versatile in its application than conventional glass window structures.

Further improvement in acoustic barrier properties may be obtained by using a modified structure as illustrated in the cross-sectional view of FIG. 5 in which one of the two plastic sheets 2 is bowed outward like a bubble to provide an enlarged chamber 3 between the two sheets 1 and 2 containing agreater mass of air or other gas which in cooperation with the edge spacing and sealing strips 4 (which preferably are of foamed or cellular material) operates to attenuate sound waves more effectively. In this form the bowed sheet 2 may form the exterior panel in a window structure. Further it will be understood that the configuration of the bowed sheet may be varied as desired to comprise various combinations of planar and curved surfaces as may seem appropriate depending on circumstances including architectural and aesthetic considerations.

While in the foregoing description and drawings there have been shown and described specific forms of edge sealing and spacing strips, it is to be understood that numerous other forms of such strips may be employed.

While the invention has been described with reference to certain specific embodiments, it will be understood that it is subject to various modifications such as will occur to those skilled in the art in the light of the foregoing disclosure and within the scope of the invention as defined by the following claims.

I claim:

1. A composite panel, particularly I an impactresistant projectile barrier, comprising:

a. a plurality of coextensive panels of tough resilient plastic material arranged in spaced parallel planes,

b. spacing means interposed between said panels at the edges thereof and comprising strips of resilient plastic material, said strips extending around the entire peripheries of said sheets and being sealed thereto by a high-strength adhesive so as to provide a freely flexible structure having an hermetically sealed enclosure between said sheets capable of withstanding the impingement of a high velocity projectile without rupturing the seals between said sheets and said strips, said enclosure being filled with an inert dry gas,

c. whereby the energy of a projectile impinging upon an outer surface of one of said sheets is dissipated by the combined action of said resilient sheets and the compression of a gas within said enclosure so as to resist passage of a projectile through said barrier.

2. A barrier according to claim 1 in which said resilient plastic sheets are formed of polycarbonate.

3. A barrier according to claim 1 in which said resilient plastic strips are formed of polychloroprene.

4. A barrier according to claim 1 in which said plastic edge strips are formed with a T cross-section, the vertical bar thereof being disposed between said plastic sheets and the two halves of the top thereof abutting against the edges of said plastic sheets.

5. A barrier according to claim 1 comprising a multiplicity of resilient plastic sheets, each adjacent pair of sheets having a strip of resilient plastic material inter posed between them at the edges thereof. extending around the entire periphery thereof and sealed thereto to provide a plurality of hermetically sealed enclosures between said sheets. said enclosures being filled with air or an inert dry gas.

- of said plastic sheets is deformed outwardly with respect to an adjacent plastic sheet to provide an enlarged compression chamber between said adjacent sheets to provide enhanced attenuation of sound waves. 

1. A composite Panel, particularly an impact-resistant projectile barrier, comprising: a. a plurality of coextensive panels of tough resilient plastic material arranged in spaced parallel planes, b. spacing means interposed between said panels at the edges thereof and comprising strips of resilient plastic material, said strips extending around the entire peripheries of said sheets and being sealed thereto by a high-strength adhesive so as to provide a freely flexible structure having an hermetically sealed enclosure between said sheets capable of withstanding the impingement of a high velocity projectile without rupturing the seals between said sheets and said strips, said enclosure being filled with an inert dry gas, c. whereby the energy of a projectile impinging upon an outer surface of one of said sheets is dissipated by the combined action of said resilient sheets and the compression of a gas within said enclosure so as to resist passage of a projectile through said barrier.
 2. A barrier according to claim 1 in which said resilient plastic sheets are formed of polycarbonate.
 3. A barrier according to claim 1 in which said resilient plastic strips are formed of polychloroprene.
 4. A barrier according to claim 1 in which said plastic edge strips are formed with a T cross-section, the vertical bar thereof being disposed between said plastic sheets and the two halves of the top thereof abutting against the edges of said plastic sheets.
 5. A barrier according to claim 1 comprising a multiplicity of resilient plastic sheets, each adjacent pair of sheets having a strip of resilient plastic material interposed between them at the edges thereof, extending around the entire periphery thereof and sealed thereto to provide a plurality of hermetically sealed enclosures between said sheets, said enclosures being filled with air or an inert dry gas.
 6. A barrier according to claim 5 in which the resilient plastic strips are joined together at their outer edges to form a unitary sealing strip for said multiplicity of plastic sheets, the portions joining said individual strip portions abutting against the edges of said plastic sheets.
 7. A barrier according to claim 1 in which at least one of said plastic sheets is deformed outwardly with respect to an adjacent plastic sheet to provide an enlarged compression chamber between said adjacent sheets to provide enhanced attenuation of sound waves. 